Fast Radio Bursts in the Era of the Vera C. Rubin Observatory's Legacy Survey of Space and Time

Abstract

Identifying the host galaxies of fast radio bursts (FRBs), and comparing their redshifts and dispersion measures, has unlocked a new probe of the cosmological distribution of ionised gas. However the necessary optical observations to identify FRB hosts, and measure their redshifts, are becoming increasingly onerous as the detection rate of precisely localised FRBs increases. Here we analyse the ability of the Legacy Survey of Space and Time (LSST), being conducted by the Vera C. Rubin Observatory, to identify FRB host galaxies, and the utility of LSST photometric redshifts for FRB cosmology. By combining a model of FRB host galaxy r-band magnitudes, $m_r$, with predictions for the FRB z-DM distribution, we create a method to predict the $m_r(z)$ distribution for the host galaxies of FRBs detected by radio surveys. We then predict these distributions for the coherent modes of the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. We find that even a single visit with Rubin will be able to identify 65% of FRB host galaxies detected by ASKAP's coherent upgrade, `CRACO'; while the final 10 year co-added images will identify 81% of those from MeerKAT's tied array beams. We also simulate the impact of using photometric redshifts for a simplified analysis to determine $H_0$, finding that estimated photo-z errors result in a decreased precision of only 7% on $H_0$ for ASKAP's CRACO system. The impact of missing dim FRB hosts, which are likely at higher redshifts, is more significant, and might degrade sensitivity to $H_0$ by 47%, or 62% when combined with photo-z errors. All told, Rubin's LSST will be an incredibly powerful survey for facilitating FRB cosmology, although supplemental observations may be useful for particularly dim and distant host galaxies.

Figures (7)

• Figure 1: Mean, and 67% ($\pm 1 \sigma$) and 95% confidence ($\pm 2 \sigma$) intervals, of the FRB r-band host galaxy magnitude distribution, $m_r$, as a function of redshift, using the FRB host galaxies analysed by Marnoch2023. Also shown for comparison are the $m_r$ magnitude limits from LSST single visit and 10 year co-adds, and FRB host galaxies (measured using a variety of filters) detected in CRAFT ICS Shannon_ICS, MeerTRAP coherent 2025AA...693A.279P, and DSA 2024Natur.635...61S2025NatAs...9.1226C observations.
• Figure 2: Fraction of FRB hosts visible to the Rubin Observatory for optical r-band limits corresponding to single visit and 10 year co-adds observations.
• Figure 3: Redshift distribution of FRBs, normalised to a peak of unity, for FRBs detected by ASKAP's CRACO system, and MeerKAT's coherent MeerTRAP mode. Also shown are the redshift distributions of FRB host galaxies accessible with a single LSST visit (dashed) and 10yr co-adds (dotted).
• Figure 4: $r$-band magnitude distribution of FRB host galaxies expected to be detected by ASKAP's CRACO system, and MeerKAT. Also shown for comparison are the magnitude limits from LSST single visits and 10 year co-adds.
• Figure 5: zDM grids and their Monte Carlo FRBs for different LSST parameters: all CRACO FRB host galaxies (top), and including both photo-z errors $\sigma_z$ and host galaxy magnitude limits $m_r^{\rm lim}$ (bottom).